Igniter for oxygen lance for thermal cutting, drilling etc.

ABSTRACT

In accordance with the method and the device according to the invention, previous pure pyrotechnic primers for initiating the ignition charges ( 6   a,    6   b ) of the oxygen lance igniters ( 13 ) are replaced by a small quantity of powdered zirconium ( 7 ). Zirconium is pyrophoric and therefore ignites, providing it has a sufficiently large surface area, in the presence of a sufficient quantity of pure oxygen, although in ordinary air it is no more flammable than ordinary wood.

The present invention relates to a new method of starting up andigniting oxygen lances mainly of the type which work without asupplementary electric arc. The invention also relates to an igniterwhich works in accordance with said method. A particular advantage ofthe method and the device (the igniter) according to the invention isthat it can be used both in the air and under water.

Oxygen lances of the type concerned here, which are used mainly forthermal cutting and drilling, and moreover under water, in scrap yardsand also within the steel industry, exist in two basic types inprinciple, the first of which and the type mainly concerned here workswith only oxygen and therefore requires some type of separate ignitionfunction, while the second main type works with oxygen and its ownsupplementary electric arc.

One problem which oxygen lances which do not have their own arc havehitherto suffered from is that they have always been difficult toignite. In oxygen lances which have their own arc, the arc is used forigniting the lance. There is also a variant in between, in which aseparate electric arc igniter is used for igniting the lance, which isthen used completely separately from the igniter as this is no longerrequired after ignition.

The difficulty of igniting oxygen lances without access to an electricarc resides in the fact that the lance tip must be heated up in anotherway to the ignition temperature of the iron, that is to say around 1050°C. Use has previously been made of a number of different methods as faras starting up oxygen lances without access to electric arcs isconcerned, and probably the two oldest methods are with an ordinary gaswelding torch or with a coal fire. However, neither of these methods hasbeen especially popular, because the person starting the lance is thencompelled to remain very close to the mouth of the lance and, if heshould happen to move too close to it, he may be struck by molten ironspray.

A somewhat more refined device or igniter for igniting oxygen lanceswhich do not have access to their own electric arc is described in SE7605274-5. The igniter described therein consists of a sleeve, open atone of its ends, of greater cross-sectional diameter than the mouth ofthe lance. The sleeve is intended to be slipped over the mouth of thelance and retained there by a spring adapted for the purpose. The sleeveitself is then at least partly filled with a metal powder and also aprimer which can be ignited via an ignition duct from the otherwiseclosed end of the sleeve. It emerges from the description that it is tobe possible to ignite the primer either by means of a notch-sensitivecomposition arranged immediately outside the closed end of the sleeve orby virtue of the ignition duct containing chemicals which themselvesignite above the ambient temperature, so that it is possible to ignitethe igniter by means of a small temperature increase. It is alsoindicated in the text that the igniter could contain pyrophoricsubstances, that is to say those which ignite when oxygen is supplied,and in that case that these would be added to the ignition compositionor primer and in this way bring about auto-ignition when the oxygensupply is opened. However, the text contains no proposals for suitablepyrophoric substances which could be used for this purpose. In quitegeneral terms, it could probably be said that to the extent that theigniter described in this patent contains such “chemicals whichthemselves ignite above the ambient temperature, so that it is possibleto ignite by means of a small temperature increase”, the igniter inquestion appears not to be capable of meeting necessary safetyrequirements because in that case it must have a strong tendency towardsaccidental ignition.

Another similar ignition device for oxygen lances is described inprinted Swedish patent application 8704421-0, in which it is stated thatthe combustion powder, that is to say the powder charge which serves forthe actual heating up to the ignition temperature of the lance, issuitably to consist of aluminium powder and that the surrounding sleeveis to be provided with a stop which regulates how far the lance can beinserted into the sleeve, and also that the latter can also contain astop mass consisting of, for example, cotton, and also that it ispossible to arrange a pyrotechnic delay between a fuse head arranged atthe mainly closed end of the sleeve and the primer arranged inside thesleeve, which is therefore in its turn to ignite the combustion powder.This arrangement is in order that the person igniting the outer primerwill be able to get out of the way. In other respects, the same commentsapply as for the device described previously, namely that, as it has tocontain not inconsiderable quantities of pyrotechnic material, thespecial provisions applying for such material must also apply for theseigniters.

Oxygen lance igniters of the general type described in theabovementioned patent specifications, with pyrotechnic charges as thestart-up medium, have been available on the market for a number ofyears, and they have in practical use been found to have a rather highfailure rate and have required no little instinctive feeling on the partof the person handling the lance with regard to knowing how rapidly toincrease the oxygen supply to full capacity.

The present invention relates then to a new type of oxygen lance igniterwhich is started up only by means of the oxygen application and whichdoes not contain any pyrotechnic primer and therefore does not have tobe dependent on any special safety regulations.

This is because, in accordance with the method and the device accordingto the invention, previous pure pyrotechnic primers for initiating theignition charges (the combustion powder) of the oxygen lance ignitersare replaced by a small quantity of pyrophoric metal powder such aszirconium or titanium. Theoretically, phosphorus which is clearlypyrophoric could also function, but phosphorus ignites in air and istherefore difficult to handle under normal conditions and thereforeunsuitable in this context. Zirconium on the other hand, which is thebest alternative in our opinion, is pyrophoric and ignites at highoxygen contents on condition that it has a sufficiently large surfacearea, but is no more flammable than ordinary wood in air, where theoxygen content is normally slightly more than 20%. It is also pertinentthat oxygen lances of the type concerned here are supplied with eithercompletely pure oxygen or oxygen mixed with small quantities of inertgas, for example roughly 5% argon, and the oxygen concentrations aremore than adequate to ignite zirconium or titanium powder with asufficiently large active surface area.

The oxygen lance igniter characteristic of the invention can thereforequite generally be said to consist of an ignition charge consisting ofmetal powder (combustion powder) which is enclosed in a sleeve, closedat one end, with an inner diameter which is greater than the outerdiameter of the oxygen lance, this sleeve being intended, when the lanceis to be started up, to be slipped over the mouth of the lance until itreaches a certain specific depth, and an initiating charge of powderedpyrophoric metal such as zirconium or titanium also being arranged inthis sleeve, in addition to the ignition charge of metal powder, on topof this ignition charge, that is to say at the end facing the oxygenlance. It is not large quantities of pyrophoric metal which are requiredfor this purpose either. If zirconium, the best alternative in ouropinion, is selected, roughly 0.05-0.5 g fine-grained pure zirconiumwith a particle size of 2-6 im is required for this purpose. Theinitiating charge rapidly ignites the ignition charge used by us in theform of 11 to 15 g of an iron/aluminium powder mixture, in which thecomponents iron and aluminium are present in the weight ratio 1:1. Wewere also able to establish that this ignition charge is most effectiveif it comprises a more fine-grained first part charge and a somewhatmore coarse-grained second part charge. Half the weight of a first partcharge produced by us of roughly 4.0 g therefore consists of aluminiumpowder with a particle size of roughly 0.1 mm, and the other half of itsweight consists of iron powder with a particle size of roughly 0.01 mm,while the second part charge consisted of 4.5 g aluminium pellets with aparticle size of 1-3 mm and 4.5 g iron filings with a particle size of0.4-0.8 mm.

With the oxygen lance igniter characteristic of the invention, it hasnow been possible to make the start-up of any type of oxygen lance notprovided with an arc as easy as should on the whole be possible. As theoxygen lance igniter does not contain any pure pyrotechnics, no specialstorage restrictions are required either. When the oxygen lance igniteris started up, the oxygen lance igniter is merely positioned in theplace intended for it over the mouth of the lance, after which theoxygen is turned on, the high oxygen content resulting in the pyrophoricinitiating charge in the form of, for example, metallic pure powderedzirconium igniting and in turn igniting the ignition charge consistingof iron/aluminium powder, which in turn starts up the oxygen/ironcombustion and ignites the lance. The reliable start-up of any oxygenlance which is achieved in this way is of course to some extent aconsequence of the high combustion temperature of the zirconium ofroughly 4900° C.

In addition to the basic idea of using a pyrophoric metal powder such aszirconium or titanium for the purpose concerned here, the invention alsoincludes a detailed design of the oxygen lance igniter itself. In thefirst place, a pyrophoric metal powder such as zirconium or titanium isrequired, and it must be held in position at the same time as asufficiently large surface area of it must be directly available forcontact with the oxygen when this is turned on. According to theinvention, we meet these requirements by placing the pyrophoric metalpowder in a gas-permeable, preferably combustible container directly ontop of the ignition charge. As the material for this container, we useordinary machine felt, from which we form a cup or container with aseparate cover of its own and an inner volume which considerably exceedsthe minimum volume which would be required for the pyrophoric metalpowder. In reality, we have found that it is advantageous if the greaterpart of the pyrophoric metal powder quite simply forms a powder coatingon the inside of the felt container. In this way, we can utilize thelarge powder surface area which is in this way made available for directcontact with the oxygen. Directly below this felt container, the actualignition charge is then arranged, preferably in the form of a morefine-grained first part mixture of iron/aluminium powder and a secondmore coarse-grained mixture of the same metals, in which connectionthese part mixtures can be the same size in terms of weight. We havealso found that there is no reason specially to separate the two partmixtures from one another but that it is entirely satisfactory if theseare filled one after the other into their common space in the igniter.On the contrary, it can even be a certain advantage if limited mixingtakes place in the boundary layer between the two part mixtures.

The invention has been defined in all its features in the patent claimsbelow, and it will now be described in only somewhat greater detail withreference to a representative design of the same shown in theaccompanying figures, in which

FIG. 1 shows a sectional inclined projection of an igniter;

FIG. 2 shows a sectional view of an igniter placed over the lance tip onan oxygen lance which is to be ignited;

FIG. 3 shows the various component parts of an igniter in an inclinedprojection and on smaller scale, and

FIG. 4 shows a sectional view of an igniter intended for underwater usemounted on a lance tip intended therefor.

Corresponding components have been given the same reference numbers inthe different figures irrespective of how and on what scale they areillustrated.

As can be seen from FIGS. 1-3, the outer part of the lance igniteraccording to the invention consists of an outer tube 1 and an innersleeve 2 which is fixed in the outer tube 1 by means of an upsetindentation 4, preferably extending all the way round, accommodated in agroove 3 in the sleeve 2. The inner sleeve 2 is also provided with aninner boring 5 in which two part charges consisting of mixtures ofiron/aluminium powder of different particle size are arranged. In thefigure, the more fine-grained part charge has the reference 6 a and themore coarse-grained part charge has the reference 6 b. Together, theseconstitute the actual ignition charge, but, in order to set this going,the initiating charge characteristic of the invention is required, whichtherefore consists of roughly 0.15 g finely divided zirconium 7 arrangedin a gas-permeable container or cup 8 provided with a cover and, in theexample shown, made from machine felt. The inner space 9 of the cup 8 isconsiderably greater than the volume of the zirconium powder 7 itself,and the powder lies freely in the space where it forms what could bedescribed as a powder coating of the inner walls of the space 9. Theinner sleeve 2 is also provided with a stop edge 10, the function ofwhich is, as shown in FIG. 2, to ensure that the oxygen lance designatedby 13 can be guided into this stop position but no further. The innersleeve 2 is also provided with two preferably somewhat resilient guidetongues 11 and 12 (see FIG. 3), the function of which is, as can be seenfrom FIG. 2, to guide the mouth of the lance 13 in eccentrically alongone inner edge of the tube 1 and also to retain it in this positionduring handling before ignition. By virtue of the positioning of thestop edge 10 between the outer end of the lance 13 and the cover of thecup 8, a gap space 14 is formed between the cover and the mouth of thelance, and this gap space is also provided with an outlet 15 locatedbetween the guide tongues 11 and 12, and this is the way the oxygen canpass through during the initial stage of the ignition process, thenpassing back through on the outside of the lance.

In order to ignite the lance, it is therefore necessary for the igniterto be slipped onto the mouth of the lance into the stop position shownin FIG. 2, after which the oxygen is turned on in the lance. Whathappens then is that the greater part of the oxygen follows the gap 14and leaves through the outlet 15 at the same time as some of the gasflows through the felt cover of the cup 8 and reacts with the zirconiumpowder which ignites and in turn ignites the ignition charge 6 whichignites the oxygen/iron reaction, and the lance is ready for use.

The variant shown in FIG. 4 of the igniter according to the inventionhas an outer casing 1 a in which the tube 1 and the sleeve 2 from thevariant shown in FIGS. 1-3 have been combined into a unit. In this unit1 a, the guide tongues 11 and 12 have been replaced by firm guideprojections designated here by 11 a. The igniter is also adapted forunderwater use and is therefore provided with an elastic sealing collar16 and could also be provided with a protective foil 17 on top of thecapsule 8 with its pyrophoric initiating charge. In such a case, thestrength of the protective foil 17 is to be adapted in such a mannerthat it is blown to pieces when the oxygen is turned on. Both theprotective foil and the sealing collar could of course also be usedabove water.

A further possible variant which is not actually illustrated in a figureis to assemble a lance part with an igniter to form a single unit. Thisvariant could be appropriate when it is mainly a large number of veryshort lances intended for use with relatively short or long breaksbetween uses which is required. One possible such area of activity couldbe work on shipwrecks.

1. Method of igniting an oxygen lance (13), characterized in that highlyconcentrated oxygen from the lance (13) is supplied to a fine-grainedpyrophoric metal powder such as zirconium (7) or titanium which igniteson contact with the oxygen and during its combustion ignites a metalpowder mixture (6 a, 6 b) and together with the latter ensures ignitionof the lance (13).
 2. Oxygen lance igniter functioning in accordancewith the method according to claim 1, comprising an ignition charge (6a, 6 b) consisting of metal powder, which is enclosed in a sleeve (1)with an inner diameter which is greater than the mouth of the lance(13), which sleeve is closed at one of its ends and is intended, beforethe lance is started up, to be slipped over the mouth of the lance untilit reaches a specific mouth position (10), characterized in that thesleeve (1) also contains, in addition to said ignition charge (6 a, 6 b)consisting of metal powder, a pyrophoric initiating charge in the formof pure metallic zirconium (7) or titanium.
 3. Oxygen lance igniteraccording to claim 2, characterized in that said initiating charge (7)consists of a pyrophoric metal powder arranged in a gas-permeable,preferably combustible container (8) which is in turn arranged betweenthe mouth position (10) of the oxygen lance (13) in the sleeve and theignition charge (6 a, 6 b).
 4. Oxygen lance igniter according to claim3, characterized in that said initiating charge (7) consists of 0.05-0.5g pure metallic powdered zirconium with a particle size of roughly 2-6μm.
 5. Oxygen lance igniter according to either claim 3 or 4,characterized in that said gas-permeable container (8), in which thepyrophoric metal powder (7) is stored at the outset, is made of porousfelt.
 6. Oxygen lance igniter according to claim 5, characterized inthat the container (8) made of gas-permeable material is designed as acup made of porous felt provided with a fully covering cover made of thesame felt material, the inner volume (9) of the cup considerablyexceeding the total volume of the pyrophoric metal powder (7).
 7. Oxygenlance igniter according to any one of claims 1-6, characterized in thatthe ignition charge (6 a, 6 b) consists of a mixture of iron andaluminium powder.
 8. Oxygen lance igniter according to claim 7,characterized in that its ignition charge (6 a, 6 b) comprises a firstmore fine-grained part charge (6 a) and a second somewhat morecoarse-grained part charge (6 b), both these part charges containingiron and aluminium in the weight ratio 1:1.
 9. Oxygen lance igniteraccording to claim 8, characterized in that the ignition charge includedtherein comprises a first part charge (6 a) containing iron powder withparticles of the order of size of 0.01 mm and aluminium particles of theorder of size of 0.1 mm and also a second more coarse-grained partcharge (6 b) containing iron powder with particles of the order of sizeof 0.4-0.8 mm and aluminium granules of the order of size of 1-3 mm. 10.Oxygen lance igniter according to claim 9, characterized in that themore fine-grained part charge (6 a) of the ignition charge (6 a, 6 b) isarranged directly adjacent to the gas-permeable container in which thepyrophoric metal powder (7) is arranged.
 11. Oxygen lance igniteraccording to any one of claims 1-9, characterized in that it consists ofan outer tube part (1) open at both ends, with an inner diameter greaterthan the oxygen lance, an inner sleeve (2) which is fixed in said outertube part by means of an upset indentation (4) accommodated in a groove(3) intended therefor and is completely closed at one end, and in whichthe ignition and initiating charges (6 a, 6 b) are inserted into aninner duct or boring (5) arranged therein, said inner sleeve (2) alsohaving at least two guide tongues (11, 12) intended to guide the mouthof the oxygen lance (13) in and hold it firmly directly above the innerduct (5) of the sleeve, and also a stop flange (10) which limits theinsertion of the lance into the sleeve to a position before it reachesthe initiating charge, and also a gas outflow opening (15) which allowsthe gas flowing out of the lance to flow out of the space directly abovethe initiating charge and back past the lance.
 12. Oxygen lance igniter(1 a) according to any one of the preceding claims, intended primarilyfor underwater use, characterized in that it comprises an elasticsealing collar (16) surrounding its end facing the lance (13) and theimmediate mouth of the lance, and also a capsule with protective foil(17) which at the outset covers pyrophoric metal powder and the strengthof which is selected in such a manner that it is blown to pieces whenthe oxygen is supplied.